5.1.2 Excretion

Question 1

What is excretion?

Answer 1

The removal of metabolic waste from the body that may build up and become toxic.

Question 2

Through which vessels does blood flow into the liver?

Answer 2

Oxygenated blood from the heart via the hepatic artery.
Deoxygenated blood from the digestive system via the hepatic portal vein.

Question 3

What is the liver directly connected to?

Answer 3

The gall bladder.

Question 4

What is stored in the gall bladder?

Answer 4

Bile salts and bile pigments.

Question 5

Where is bile released into?

Answer 5

The duodenum via the bile duct.

Question 6

What is the bile duct?

Answer 6

Duct that carries bile secreted from the liver to the gall bladder.

Question 7

How is the liver divided?

Answer 7

The liver is composed of liver lobules which are cylinders made of hepatocytes arranged in
rows, connected at the centre.

Question 8

What cells make up liver lobules?

Answer 8

Hepatocytes.

Question 9

How are hepatocytes separated from each other?

Answer 9

Connective tissue.

Question 10

What is the vein called in the middle of the lobule and what is it connected to?

Answer 10

The central vein which is connected to the hepatic vein.

Question 11

In what vessel does blood from the vein and arteries mix?

Answer 11

Sinusoids

Question 12

Purpose of blood passing through sinusoids.

Answer 12

Puts the blood in close contact with liver cells.

Question 13

Which vessel drains blood from the liver?

Answer 13

The hepatic vein

Question 14

What do kupfer cells do?

Answer 14

Break down red blood cells.
Destroy any pathogens

Question 15

Where are kupfer cells found?

Answer 15

Sinusoid walls.

Question 16

What is the portal triad composed of?

Answer 16

Hepatic artery
Hepatic portal vein
Bile duct

Question 17

Function of hepatocytes.

Answer 17

Store glycogen
Form urea
Detoxification

Question 18

How does the liver help to regulate blood glucose concentration.

Answer 18

Constant conversion of glucose to glycogen and vice versa.

Question 19

How is urea formed?

Answer 19

The protein in our diets is digested as amino acids which are absorbed and transported in the liver.
Excess amino acids are deaminated so that the rest of the molecule can be used.
The amino group is removed with an extra hydrogen atom and these combine to form ammonia which forms ammonium ions in the cytoplasm.
The remaining keto acid may enter the krebs cycle to be respired, converted into glucose or converted into glycogen.
Ammonia can be converted into urea by combining it with co2 via the ornithine cycle.
One urea molecule is formed from one molecule of co2 and two amino groups.

Question 20

Explain the ornithine cycle.

Answer 20

1) ammonia is combined with ornithine and c02 (releases a molecule of water) to produce citruline.
2) Ammonia is added to citruline to produce arginine (releases another molecule of water).
3) Urea is removed from citruline which reforms ornithine and the cycle begins again.

Question 21

What is deamination?

Answer 21

When the amine/amino group is removed from an amino acid to form ammonia and keto acid.

Question 22

How does detoxification of ethanol work?

Answer 22

1) Ethanol is broken down into ethanal which is broken into acetic acid.

Question 23

Give an example of things that the liver breaks down during detoxification.

Answer 23

Paracetamol
Ethanol
Insulin
Hormones

Question 24

What is cirrhosis of the liver?

Answer 24

When liver cells die.

Question 25

How does the liver metabolise lactate?

Answer 25

lactate is converted to pyruvate. Some of this pyruvate enters the mitochondria to be respired anaerobically to convert to glucose. Some of this glucose is stored as glycogen and the remaining glucose enters the blood to maintain blood glucose concentration.

Question 26

Where does the lactate that the liver metabolises come from?

Answer 26

The end product of anaerobic respiration.

Question 27

When does fatty liver occur?

Answer 27

The metabolism of ethanol generates a large amount of ATP. Hepatocytes do not metabolise as much fat as usual when this ATP is created and instead store the fat which leads to the condition known as fatty liver.

Question 28

List some functions of the liver?

Answer 28

Glycogen storage
Detoxification of harmful substances
Lactate metabolism
Hormone metabolism
Formation of urea